Technical Field
The present invention generally relates to composite carbon materials, methods for making the same and devices containing the same.
Description of the Related Art
Lithium-based electrical storage devices have potential to replace devices currently used in any number of applications. For example, current lead acid automobile batteries are not adequate for next generation all-electric and hybrid electric vehicles due to irreversible, stable sulfate formations during discharge. Lithium ion batteries are a viable alternative to the lead-based systems currently used due to their capacity, and other considerations. Carbon is one of the primary materials used in both lithium secondary batteries and hybrid lithium-ion capacitors (LIC). The carbon anode typically stores lithium between layered graphite sheets through a mechanism called intercalation. Traditional lithium ion batteries are comprised of a graphitic carbon anode and a metal oxide cathode; however such graphitic anodes typically suffer from low power performance and limited capacity.
Silicon, Tin, and other lithium alloying electrochemical modifiers have also been proposed based on their ability to store very large amounts of lithium per unit weight. However, these materials are fundamentally limited by the substantial swelling that occurs when they are fully lithiated. This swelling and shrinkage when the lithium is removed results in an electrode that has limited cycle life and low power. The solution thus far has been to use very small amounts of alloying electrochemical modifier in a largely carbon electrode, but this approach does not impart the desired increase in lithium capacity. Finding a way to increase the alloying electrochemical modifier content in an anode composition while maintaining cycle stability is desired to increase capacity. A number of approaches have been utilized involving nano-structured alloying electrochemical modifier, blends of carbon with alloying electrochemical modifier, or deposition of alloying electrochemical modifier onto carbon using vacuum or high temperature. However none of these processes has proven to combine a scalable process that results in the desired properties.
Hard carbon materials have been proposed for use in lithium ion batteries, but the physical and chemical properties of known hard carbon materials are not optimized for use as anodes in lithium-based batteries. Thus, anodes comprising known hard carbon materials still suffer from many of the disadvantages of limited capacity and low first cycle efficiency. Hard carbon materials having properties optimized for use in lithium-based batteries are expected to address these deficiencies and provide other related advantages.
While significant advances have been made in the field, there continues to be a need in the art for improved hard carbon materials and for improvements to the approaches used for incorporating alloying electrochemical modifiers into these carbons in order to result in the desired material properties and electrochemical performance needed in electrical energy storage devices (e.g., lithium ion batteries). The present invention fulfills these needs and provides further related advantages.